Mechanical Technology

Mechanical Technology — October 2015

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Hydraulic and pneumatic systems

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The vehicle and equipment arm of Highpoint Vacuum

now has a production capacity of more than 20 vehicles

per year.

filters, for example, a little moisture will

trigger the reaction to set the cement

and destroy the filter. This has really

happened! That is why we have the elec-

tronic monitoring system fitted, to protect

the truck from costly damage,” he says.

HPVR Combis

Designed for combined jetting and

vacuum applications, such as municipal

sewer and line cleaning, Highpoint’s

Vacuum trucks can also be used for

vacuum applications such as emptying

industrial sumps and slurries, removing

toxic waste, and wet and dry ash removal

from power station boilers.

“In the rainy season, a lot of mud and

silt accumulates in the drains, which

cannot be carried away by subsequent

liquid flows. To clean this from the drain,

we use a retrojet nozzle, which has more

jets pointing backwards that forwards,”

Visser explains. Typically, this nozzle

is fitted to the end of a 120 m sewer

cleaning hose on a hydraulically driven

hose reel behind the truck. “This jetting

nozzle is placed down a manhole into the

drain line. Water is pumped through the

nozzle at about 200 bar and, because

there are more jets pointing backwards

than forwards, a net forward thrust is

generated. This propels the jet and hose

up the drain towards the next manhole.

“Once there, the hydraulic reel is acti-

vated to withdraw the hose, causing any

sediment to be washed down towards the

entry point, where a separate vacuum

tube sucks the waste and water back

up into the truck, allowing it to be safely

disposed of at an appropriate dump or

sewage plant,” Visser says.

When using a traditional Combi truck,

according to Visser, the operator might

spend a third of each day looking for

water from fire hydrants, for example,

refilling and returning to the manholes.

Overcoming this problem is the com-

pany’s recently released Recycler, which,

in addition to all of the features of its

traditional Combi trucks, also includes

an onboard system to filter the water

from the waste so that it can be reused

for jetting. “The water recycling system

itself is sourced from Dietmar Kaiser, but

all of the rest is built here in our facility

just outside of Sasolburg,” he adds.

The hydraulic door clamping

system

All Highpoint vehicles contain a range of

hydraulic pumps and circuits to support

the vehicles’ functions. A particularly

sophisticated hydraulic system is used to

handle the opening, closing and clamp-

ing of the tank door. “These vehicles are

emptied like tipper trucks. The back door

opens and a hydraulic ram raises the

cab end to discharge the tank’s contents

through the door at the back. But in op-

eration, the tank needs to be well sealed

to hold the vacuum. We use six hydraulic

clamps around the rear door seal. Each

of these each has an interlock and a hy-

draulic cylinder for opening and closing

the clamp mechanism. And when open,

hydraulically actuated hooks secure the

door to allow people to safely enter the

tank to clean it,” Visser says.

The clamping and interlocking system

is operated via a hydraulic sequencing

circuit that uses a manifold block with

Sun Hydraulics cartridge valves. “We

use kick-down valves, which deliver a

pressure spike as a circuit is completed.

By designing the system to produce

spikes at the appropriate pressures, we

achieve a very robust cascade activation

sequence,” he explains.

“The clamps open in the first hydrau-

lic sequence. Then the door opens and,

finally, the safety lock engages – and the

sequence control is 100% mechanical.

We do not depend on any electronic

controllers.”

The system also has an equivalent

reverse sequence to close the door again,

with the lock releasing, the door closing

and the clamps re-engaging. This is

achieved via a separate hydraulic circuit

built into the same manifold block. “Both

sequences are fully automatic, so an

operator cannot close the door while the

lock is still engaged, for example, which

would damage the mechanisms.

“Sun Hydraulics cartridge valves

are so accurate that you can activate

them during a half cycle. If the door is

half open, the system can be put into

reverse, which will close the door safely

in the reverse sequence. Nothing needs

to be reset. The sequence simply trig-

gers immediately on activation,” he tells

MechTech

Highlighting the advantages of using

hydraulic controls, Visser relates that the

Highpoint HPVR 1000s typically work at

acid plants and in petrochemical compa-

nies, which are highly corrosive environ-

ments. “Exposed electrical connections in

these environments will corrode, making

the vehicle unreliable.

“The nice thing about hydraulic con-

trols is that the whole system is hermeti-

cally sealed and 100% protected from

outside influences. Everything is running

in very clean oil, which makes it ideal

for use in dirty, corrosive and aggressive

environments. We also use hydraulics

for most of the physical actuation tasks,

such as the tank tipping and aligning

the hose reels, with pneumatic actuators

for the valves. But we try to stay away

from PLCs as much as possible on the

industrial vehicles,” he says.

“When we have to use electronic

controllers, for municipal vehicles, for

example, we use IFM-controllers, a

German specialist in mobile electronics

that manufactures 100% sealed IP65-

rated, so they are not prone to dust or

moisture ingress,” he adds.

“Like-for-like, our vehicles are about

20 to 30 % cheaper that imported

equivalents. Compared to our European

competitor, our trucks are at least R1.5-

million cheaper and, more importantly,

our turnaround times are much better. If

ordering from Europe, first, you are forced

to use a MAN truck, which is already

about R400 000 more expensive than

the UDs we use, and we can deliver

in four months, from order to delivery.

In addition, we can offer unparalleled

turnaround times on spares and repair,”

Visser concludes.